1998.5 Dodge Club Cab 2500HD 4x4 auto trans (24-valve Cummins) bought new: Truck sat for quite a while until I could get the $$$ for a top-of-the-line VP44 -- I've already been thru 3 stock/rebuilts! Everything was working before the last pump died & now the truck is running great, but the O/D off button @ the end of the shift lever doesn't work -- the truck shifts like it should, including into overdrive, I just can't turn the overdrive off.

Also, while the cruise control light on the dash comes on, the cruise will not set. Going thru all the comments I could find, I did track down the vacuum line under the battery on the driver's side & sure enough it was broken, but I've fixed that. Also, I've had the cover off where the 3 cables go (throttle, trans & cruise) to adjust the cable going to the trans & as far as I can tell, everything is connected properly.

So I'm assuming both problems are in the electronics & I really don't know where to look. I know these trucks are VERY sensitive to voltage & connections, especially @ the batteries & I've wire-brushed, sprayed with contact cleaner, etc. every connection I can get my hands on & both batteries are good. I've also looked for anything amiss in the wiring harnesses & I don't see anything there.

So this old mechanical engineer is calling on you new-fangled electronics guys for some ideas on where to look & what to look for!!

 

Welcome to DB!

Just to touch quickly on you VP's dying, do you have an aftermarket lift pump and fuel pressure gauge? The problem will keep happening if the transfer pressure isn't good.


Hopefully us young-ins will get yer electronics figured out. Of course, simple stuff first. All fuses and relays are good? I'm wondering if you have an issue with your brake light switch. Here is a diagram of the Cruise solenoid, PCM, and brake switch:

 

Thanx a million for the diagram !!! Yes, I have an aftermarket lift pump which I've tested & holds a constant 15 psi. I do not have a gauge in the truck (yet) but I plan to add a side-pillar setup with 3 gauges, lift pump fuel pressure, boost & exhaust temp.

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Oooops -- forgot to answer that question & yes, they all are good -- did a continuity test on all of 'em !! I have a good test meter & can track down electrical problems, but electronic circuits, software & the like which did not exist when I went to college in the '70's I do not know.